As photography has changed and expanded, so has the gallery: its cafe and bookshop were invariably packed, but it was always too much cafe, not enough gallery. In 2008, it moved to a woefully inadequate, low-ceilinged former textile warehouse behind Oxford Circus. It was a dismal corner, an area of blank walls and unloved pavements that did not appear a step up in the world.

The gallery closed for refurbishment two years ago – and reopens on Saturday. I was not optimistic. But by doubling the gallery space with a two-storey extension, Irish architects O'Donnell and Tuomey have done a terrific job. The building is elegant, airy, and lets you focus on the work. Two new layers of high-ceilinged galleries have been added, meaning photography, film, video and digital imagery, as well as works that demand controlled humidity and light levels, can finally be shown in the right conditions.

Dennis Gilbert/View

With its cutaway black rendering, stretches of the original, late-Victorian patterned brickwork and a wraparound ground-floor window, not to mention floor-to-ceiling windows on the upper storeys that stop you thinking you're standing in a box, the £9.2m renovation is more than a mere makeover. The ground-floor glass is being referred to as "the Edward Hopper window", after the American's 1942 painting Nighthawks, a depiction of a desultory late-night diner. Late-night dive or not, the gallery still has a cafe fixation.

A digital wall, currently showing artworks based on antediluvian 1987 GIF image file technology, reminds us how much photography has changed and goes on changing. The photographer in a fishing vest, Hasselblad in hand, is fast becoming extinct. Everyone is a photographer now, but photography means many things. Just as darkrooms close and film becomes unavailable, photography itself has become the most ubiquitous and democratic medium of all. As it races on, the new gallery is trying to keep up.